Long-term objectives are to understand how the optical structures and photoreceptor cells influence and limit the visual information provided to the nervous system by the receptor axons. Determine the basic principles for processing of spectral, spatial, and polarization information. Develop noninvasive, optical methods for monitoring physiological and photochemical processes of photoreceptor cells in eyes of completely intact, healthy insects. Specific aims are to characterize the visual pigment cycle of butterflies, and evaluate the butterfly as an animal model for the visual pigment cycle of the human; develop a noninvasive, optical method for monitoring turnover of photoreceptor membranes; characterize the kinetics of metarhodopsin's decay and rhodopsin's recovery at physiological temperatures; determine the mechanism for bleaching of the rhabdom; determine if light is a necessary cofactor for reisomerization of all-trans retinoid to 11-cis; compare electrophysiological and optophysiological methods for monitoring receptor sensitivity; characterize the development of rhodopsin titer, volume of receptor membrane, and receptor sensitivity in the developing butterfly eye. Methodology includes intracellular optical physiology, ERG, computer-controlled retinal microdensitometry, High Performance Liquid Chromatography, freeze-fracture and transmission electron-microscopy, electromagnetic theoretical modeling and computer simulation. The health-related importance of this basic research is the improved understanding of fundamental visual mechanisms. The rationale for working with insects is the important experimental advantages their compound eyes offer, making it possible to measure physiological and photochemical properties of photoreceptor cells in eyes of completely intact and healthy animals. The butterfly may serve as a useful animal model for the visual pigment cycle of humans.